The Campaign Builder's Guild

I was wondering how multiple, say, three, moons would affect the tides and therefore sailing in general.

Any thoughts?

Whoa, that's a really interesting question. I've never thought of that.

I imagine the tides would more-or-less even out, with the most obvious "tide" being affected by the largest moon, and a "mini-tide" for each of the smaller moons. Because of the "mini-tides", there probably won;t be such a pronounced contrast between the (main) tide coming and and it going out.

I'm not really sure how this would affect sailing in general, though...

The Long Answer: It depends on the mass and orbiting distance of each moon (and the sun!), and the way all those objects line up while they orbit (and are orbited around.)

Real Earth tides arise out of an interaction between lunar and solar gravitational pull, and are different depending on whether the angle between the moon and sun allows their gravity effects to amplify each other or conflict with each other. A multi-moon planet would have similar gravity interactions, just much more complicated.

The Short Answer: However you want to make it work, if at all. I've got to give you points for going the extra mile toward gritty realism, but I think that calculating the effects of even one moon on the tides in any meaningfully quasi-scientific way is a little more work than it's worth.

My advice is that you decide on whatever interesting tides/sailing ideas you want to implement, implement them, and then say "it is because there are three moons that this happens the way it does." Really, who's going to contradict you?

Your short answer isn't that much shorter than your long answer.
 :poke:  ;)

Haha. It should be "The Satisfying Answer" and "The Answer You'll Go with."

I'd guess that it would be sorta like the asteroid belt in the Solar System, where they are pulled on mostly by the sun, but Jupiter has an effect on some of them, as welle.

Something I've used (and you can see this in Khoras, too), is that at regular intervals (every 11 years in Khoras), your moons will be in alignment and create fantastic storms.

Quote from: Phoenix KnightSomething I've used (and you can see this in Khoras, too), is that at regular intervals (every 11 years in Khoras), your moons will be in alignment and create fantastic storms.

Yeah I was thinking something along those lines.  When the moons lined up properly there would be a "supertide" that would cause huge tidal waves.  Also, there would probably be extended periods of low tide as well that opens up large beach areas and in some cases cliff faces that were once part of the sea shelf.  I would say you should probably mention some of these things, but not go into huge detail on them, as 9 out of 10 times they won't affect game play.  It would make for an interesting campaign, and in some cases might affect sea ventures, but still, this would for the most part be background.

What might be interesting to do would be to have the alignment of the three moons create a sort of mystical field that functions rather like the Bermuda Triangle, but it would sort of drift based on the positions of the moon.  Actually though, that would be really hard to work out if the moons orbit the earth at a speed even remotely similar to our own.

To quote J. Michael Straczynski (spelling is probably WAY wrong, but creator of Babylon 5), your tides should work "at the speed of plot."

If you need the tides to be wrong for some reason, they can can be wrong, and you can blame it on the moons.

Quote from: psychoticbarberTo quote J. Michael Straczynski (spelling is probably WAY wrong, but creator of Babylon 5), your tides should work "at the speed of plot."

If you need the tides to be wrong for some reason, they can can be wrong, and you can blame it on the moons.

One of my favorite quotations.


Also, the Bermuda Triangle idea is cool.

Something to note: In our solar system Earth's moon is the second largest relative to the mass of the planet it's orbiting. Pluto's moon Charon is number one, and it's so massive that they actually orbit around eachother.

If you're going to create a planet where the moons, when aligned, cause such huge tides compared to what we have on earth, then there's also a good chance that that same alignment could possibly alter the planet's orbit slightly.


Just some food for thought.

Quote from: PellanorSomething to note: In our solar system Earth's moon is the second largest relative to the mass of the planet it's orbiting. Pluto's moon Charon is number one, and it's so massive that they actually orbit around eachother.

If you're going to create a planet where the moons, when aligned, cause such huge tides compared to what we have on earth, then there's also a good chance that that same alignment could possibly alter the planet's orbit slightly.


Just some food for thought.

Which would mean thrice as many solar eclipses, and times when the moons eclipse each other.  This could have effects on more than just sailing and the tides.

Well, as a physicist I guess I have an obligation to have a go at this. Even though a lot has been said already, and I'll be repeating some of it.

Zero order, the orbital dynamics of a large collection of moons is fantastically complicated. Typically some orbital resonance effects will cause them to eventually organize into patterns. (Like, this moon orbits five times for every two orbits of this other one.) But even there, if there are more than two moons, you can have some pretty complicated interactions.

Next, the obvious question is how different the moons are in size. If one is largest and the others are much smaller, you'd mostly have the tides of the largest one, with some variation in height of tide depending on how the smaller ones line up. If the moons are similar in size and orbit, you could have much more complicated interactions, where tides could effectively be cancelled out in some phases and enhanced in other phases.

The easiest scenario to contemplate would be one dominant moon and one secondary moon. I'll assume they orbit in more-or-less the same orbital plane and in the same direction, which is physically realistic, but not obviously necessary in a fantasy world. For example, let's say the secondary moon orbits one-and-a-half times for every orbit of the dominant:

If they are aligned at the new moon (new moon for the dominant, that is), there will be enhanced tides. As they orbit, they'll slowly fall out of alignment and the size of tides will reduce. By the full moon, they'll be 90 degrees out of alignment and tides will be "normal".

The next new moon, they'll be opposed, and tides will be at their minimum. Then they'll start to fall out of alignment, leading to normal tides again by the next full moon. Then, by the third new moon, they'll be aligned and enhanced again.

You see this gives a pattern: Normal tides at full moons, and alternating enhanced or reduced tides at the new moon. Interactions with the planet's solar orbit would cause this pattern to slowly shift over time so the maximum and minimum tides wouldn't necessarily always occur at the new moon, but you get the idea.

If there are multiple secondary moons, then much more complicated patterns would arise. If you want to go with something like this, I'd suggest having some kind of College of Lunology in the more advanced civilizations. These experts have studied the moons and have charts, tables, divinations, etc. to predict the moons and tidal variations. For non-experts, it would all seem pretty random, so you can just insert whatever random tidal variations support your story. If characters need to know, they'd have to consult a Lunologist (or take levels in Knowledge [Lunology]).

As for affecting sailing:

Strong tides can create huge tidal bores, with strong currents, whirlpools, and the like. At times of especially strong tides, certain areas might be effectively unnavigable, or you might have to wait for a small window of quiescence during the time the tide is turning around. This would tend to happen in areas of narrow straits or long, narrow bays. (Some of the strongest tides on our planet occur in the Bay of Fundy near Nova Scotia. The bay is long and gradually narrows, so the tidal waters gain momentum coming up the bay and are then squeezed into a smaller and smaller space, to create extremely high tidal variations.)

You could also have unusually extended tidal flats in some areas. During the most enhanced tidal phase, the shoreline could easily vary by a mile or two between the high and low tide. Whereas during the suppressed tidal phase, it might hardly vary at all. Such a case might require a very extensive series of piers and stilt buildings if they were to have any boating at all.